Arrangement for the outlet nozzle of a submerged plasma torch dedicated to waste treatment

ABSTRACT

An injection and cooling system configured to equip a plasma torch, a plasma torch equipped with the system, an installation for treatment of a liquid solution including such a plasma torch, and a method for treatment of a liquid solution by injection into a plasma generated by such a plasma torch submerged in a different liquid solution.

FIELD OF THE INVENTION

The present invention relates to the field of the treatment of waste such as advantageously liquid chemical waste.

More particularly, the present invention relates to the arrangement of the outlet nozzle of a submerged plasma torch by installing a liquid injection system and adding an adapted combustion gas cooling system. As such, the present invention proposes an injection and cooling system intended to equip a plasma torch, the plasma torch equipped in this way as well as an installation and a method for the treatment of a liquid solution comprising or using such a plasma torch.

STATE OF THE RELATED ART

The treatment of liquid waste of all kinds such as organic, hazardous and/or radioactive waste is currently performed by means of thermal methods involving furnace type reactors which may be of different types such as static furnaces or rotary furnaces, heated by various means.

As such, the waste treatment methods implement thermal units connected to relatively substantial gas treatment systems to carry out the cooling, filtration and neutralisation of certain elements such as chlorine. This generally results in large-sized units subject to high temperatures. The presence of certain elements such as chlorine, phosphorus, sulphur, etc. subject to these high temperatures exacerbates the corrosive properties of the gases, which forces manufacturers either to choose superalloys which are often very costly, or to accept frequent replacement of certain parts of the method.

The reactors involved may be of different types. They may consist of furnaces heated by the Joule effect, by plasma torches or by the combustion of gas fuels such as propane. The temperature of the treatment can thus vary according to the nature of the load. If, for example, it consists of dodecane type hydrocarbons, this load may develop a thermal power of approximately 10 kW per l/h, which needs to be discharged. If, on the other hand, it consists of an aqueous solution, the power of the plasma will be partially used for the evaporation thereof. The temperature behaviour of the reactor involved in the method is thus substantially impacted by the nature of the liquid to be treated.

According to the method, the introduction of the liquids may vary. Either they are introduced into the heart of the hot spot of the furnace, or they are introduced into the power source. For example, they can be evaporated in the fuel gas or introduced directly into a plasma. They can be treated alone or in a mixture with solids according to the circumstances. By way of example, the patent application EP 0,469,737 proposes a method and a device for the treatment of liquids in an air plasma [1]. In this example, the plasma burns in a refractory reactor and the liquids are introduced into the gas stream generating the plasma. Such a method requires a relatively cumbersome device as the gases produced must be treated via scrubbing columns in particular.

Furthermore, regardless of the method used, it would appear that the nature of the liquids can vary substantially for heat emission reasons but also for reasons of compatibility with the materials chosen to produce the reactor.

A number of solutions to the problem of waste treatment involving the use of submerged plasmas have previously been proposed. For example, mention may be made of the publication by N. V. Alekseev et al reporting a treatment method wherein a plasma flows into a receptacle containing an aqueous solution polluted with a few tens of mg of phenol per litre of water [2]. In this case, the plasma serves to produce hydrogen dioxide which oxidises the dissolved organic compounds. The publication by G. Fortin et al also mentions a method involving an argon/nitrogen plasma torch, burning at the bottom of a reactor filled with cyanide-charged leachates [3]. An international application has further been filed by the same authors to protect the invention [4].

In any case, these methods have been developed to treat aqueous solutions containing small quantities of substances to be removed: a few ppm of phenol in the first case, a few ppm of cyanides in the second. The substances are degraded progressively by the plasma torch operating at the core of the solution, said torch producing the chemical radicals required for the oxidation of the organic compounds.

Recently, the international application WO 2011/064361 proposed a method for the treatment of chemical waste, particularly liquid waste, enhanced in terms of speed and efficiency, suitable for the treatment of liquids, regardless of the nature and/or composition thereof, using a device which is simpler, more compact and less costly in the production and/or use thereof [5]. The principle of the method described in this international application is based on a blown arc plasma torch wherein a liquid to be treated is introduced. This plasma torch such that an oxygen plasma, positioned at the bottom of a reactor filled with a solution different to the liquid to be treated and particularly filled with water carries out the combustion of the organic compounds introduced therein; it produces gases which are directly quenched and scrubbed.

This technique offers various advantages which are: (i) the very rapid quenching of the gases preventing the formation of undesirable compounds such as dioxins or furans; (ii) the direct handling of potentially corrosive elements such as, for example, chlorine, fluorine and phosphorus, by neutralisation in the solution different to the liquid to be treated and particularly in water; (iii) direct prefiltration of the gases by bubbling through a certain height of water; and (iv) the system remaining generally cold which enables it to be readily protected from corrosion risks.

As such, the method described in the international application WO 2011/064361 makes it possible to carry out rapid degradation of organic liquids with destruction efficiencies close to 99.98% during the treatment of 1 L/h of phosphorus-containing hydrocarbon.

Furthermore, the international application WO 2011/064361 describes a part placed at the end of the plasma torch forming an additional combustion zone and suitable for having two different types of channels, one suitable for conveying oxidant gas and the others for introducing the solution to be treated into the core of the plasma.

Research has been conducted in order to extend the operating range and increase the treatment rate which has made it possible to achieve good degradation yields with however combustion gases wherein the quality can be very variable according to the products treated. In some cases, the CO content in the gases can be close to 10% which requires, in the light of emission standards, either the installation of a post-combustion chamber at the reactor outlet, or the exclusion of certain liquids from the treatment range.

The inventors thus set themselves the aim of enhancing the method described in the international application WO 2011/064361 further so as particularly to increase the quality of the gases released while increasing the organic compound destruction efficiency further.

In other words, the inventors set themselves the aim to propose a technological enhancement conducted with a view to optimising the nature and the composition of the gases before they are quenched in the reactor solution, such as water, in the core of which the treatment plasma is submerged.

DESCRIPTION OF THE INVENTION

The aims set and others are achieved by the invention which proposes substantially modifying the outlet geometry of the submerged torch and, more particularly, adding at the plasma torch outlet a plurality of stages in order to ensure optimal destruction of the organic matter accompanied by fully oxidised combustion gas production.

FIG. 1 recalls in the right part thereof the concept of the method described in the international application WO 2011/064361 and provides in the left-hand insert a view of the parts added at the plasma torch outlet and which represent the very focal point of the invention.

This assembly successively comprising an injection device, an oxidising dilution device, a reinjection device and a cooling device makes it possible to ensure full and rapid oxidation of the gases from the method and obtain compositions for these gases in accordance with the various emission standards. As such, the present invention relates to an injection and cooling system, intended to equip a plasma torch, having a cavity intended to contain plasma and combustion gas and comprising:

-   -   a first injection device devised to (intended to) inject, into         said cavity, a liquid solution to be treated hereinafter         referred to as solution S₁,     -   a second injection device arranged against said first injection         device and devised to (intended to) inject, into said cavity, an         oxidant gas,     -   a cooling device devised to (intended to) cool the gas(es)         contained in said cavity, said system comprising a third         injection device inserted between said second injection device         and said cooling device and devised to (intended to) inject,         into said cavity, a liquid solution different to the liquid         solution to be treated hereinafter referred to as solution S₃         and said four devices being hollow, coaxially aligned and         defining said cavity.

In other words, the enhancement according to the present invention is based on the arrangement of the nozzle outlet of the plasma torch which has been equipped with 4 technological elements placed on top of one another and which are:

-   -   a first device or stage for injecting the liquid to be treated         devised to convey same as close as possible to the plasma flame:         introducing the liquid to be treated and particularly organic         liquids as close as possible to the plasma ensures         volatilisation and rapid pre-oxidation of the chemical compounds         present in this liquid;     -   a second device or stage for injecting oxidant gas enabling         re-enrichment with oxygen which guarantees stoichiometric         conditions and enhances the oxidation of the chemical compounds         and the combustion of the treatment gases;     -   a third device or stage for injecting liquid other than the         solution to be treated guaranteeing rapid cooling of the gases         to a temperature level required for an equilibrium shift in         favour of superior oxidation of the gases and thus favourable         for emission standards; and     -   the final device or stage for cooling at the end of the reaction         providing a sufficient dwell time for the gases so as to enable         the finalisation of the reactions and achieve the chemical         equilibriums sought which makes it possible to optimise         combustion before quenching the gases in the reactor solution.

Within the scope of the treatment of liquid waste, the advantages offered by the injection and cooling system according to the present invention essentially relate to the organic compound destruction efficiency and the gas emission quality. Furthermore, besides the advantages associated with the enhancement provided by the injection and cooling system according to the invention, those intrinsic to the method described in the international application WO 2011/064361 are also found, i.e. the destruction of a solution to be treated injected into the core of a plasma burning in a solution different to the solution to be treated and particularly in water, quasi-instantaneous quenching of the gases in water, quasi-instantaneous condensation of volatile substances, dust extraction from the gases by means of a scrubbing effect and neutralisation of the gases during bubbling.

The first injection device of the system according to the invention, devised to (intended to) introduce, into said cavity, the solution S₁ to be treated comprises at least one first channel leading to said cavity and devised to (intended to) convey said solution S₁ therein. This device may comprise at least two first channels, at least three first channels, or at least four channels leading to said cavity and devised to (intended to) convey said solution S₁ therein.

The first channel(s) may have any orientation. They may be oriented towards the plasma outlet orifice, towards the second injection device or perpendicularly to the plasma torch axis. The first channels may all have the same orientation or at least two different orientations. However, as an advantageous alternatively, the first channel(s) are all oriented towards the plasma outlet orifice.

This first device is advantageously made of a material suitable for the solution S₁ to be treated. Such a material is typically a metal such as copper or an alloy, particularly a non-oxidising alloy such as stainless steel or an alloy based on nickel and chromium and comprising at least one element chosen in the group consisting of iron, molybdenum, manganese, niobium and copper, particular examples of such alloys being marketed under the brand Inconel. Such a material may also be a ceramic. Furthermore, this first device may have internal water circulation cooling means.

The second injection device of the system according to the invention, devised to (intended to) introduce, into said cavity, an oxidant gas comprises at least one second channel leading to said cavity and devised to (intended to) convey said oxidant gas therein. This device may comprise at least two second channels, at least three second channels, or at least four second channels leading to said cavity and devised to (intended to) convey said oxidant gas therein.

The second channel(s) may have any orientation. They may be oriented towards the first injection device, towards the third injection device or perpendicularly to the plasma torch axis. The second channels may all have the same orientation or at least two different orientations. However, as an advantageous alternative, the second channel(s) are all oriented towards the third injection device.

This second injection device is advantageously made of a material suitable for the solution S₁ to the treated. Such a material is typically a metal such as copper or an alloy, particularly a non-oxidising alloy such as stainless steel or an alloy based on nickel and chromium and comprising at least one element chosen in the group consisting of iron, molybdenum, manganese, niobium and copper, particular examples of such alloys being marketed under the brand Inconel. Furthermore, this second device may have internal water circulation cooling means.

The third injection device of the system according to the invention, devised to (intended to) introduce, into said cavity, a liquid solution different to the liquid solution to be treated hereinafter referred to as solution S₃ comprises at least one third channel leading to said cavity and devised to (intended to) convey said solution S₃ therein. This device may comprise at least two third channels, at least three third channels, or at least four third channels leading to said cavity and devised to (intended to) convey said solution S₃ therein.

The third channel(s) may have any orientation. They may be oriented towards the second injection device, towards the cooling device or perpendicularly to the plasma torch axis. The third channels may all have the same orientation or at least two different orientations. However, as an advantageous alternative, the third channel(s) are all oriented perpendicularly to the plasma torch axis.

This third injection device is advantageously made of a material suitable for the solution S₁ to be treated. Such a material is typically a metal such as copper or an alloy, particularly a non-oxidising alloy such as stainless steel or an alloy based on nickel and chromium and comprising at least one element chosen in the group consisting of iron, molybdenum, manganese, niobium and copper, particular examples of such alloys being marketed under the brand Inconel. Furthermore, this third device may have internal water circulation cooling means.

The cooling device of the system according to the present invention devised to (or intended to) cool the gas(es) contained in said cavity have a sufficient length to ensure complete and optimal oxidation of the organic load present in the solution to be treated. Advantageously, said cooling device comprises at least one sheath cooled by internal water circulation.

Furthermore, this cooling device is advantageously made of a material suitable for the solution S₁ to be treated. Such a material is typically a metal such as copper or an alloy, particularly a non-oxidising alloy such as stainless steel or an alloy based on nickel and chromium and comprising at least one element chosen in the group consisting of iron, molybdenum, manganese, niobium and copper, particular examples of such alloys being marketed under the brand Inconel.

In the injection and cooling system according to the present invention, at least one injection device chosen in the group consisting of the first injection device, the second injection device and the third injection device comprises internal water circulation cooling means. In one particular embodiment, at least two of these devices comprise internal water circulation cooling means. As such, the first and second injection devices, the first and third injection devices or the second and third injection devices comprise internal water circulation cooling means. In one even more particular embodiment, the first, second and third injection devices comprise internal water circulation cooling means.

The present invention also relates to a plasma torch equipped with an injection and cooling system as defined above. Any plasma torch, particularly any arc plasma torch and, in particular, any blown arc plasma torch is suitable for use within the scope of the present invention. The power and intensity of the plasma torch according to the present invention will be chosen according to the solution S₁ to be treated and according to the flow rate to be injected.

The present invention further relates to an installation for the treatment of a liquid solution S₁ comprising:

-   -   a plasma torch equipped with an injection and cooling system as         defined above;     -   a container of liquid solution S₁;     -   first means devised to convey the liquid solution S₁ from said         container of liquid solution S₁ to the first injection device of         said injection and cooling system;     -   a container of oxidant gas;     -   second means devised to convey the oxidant gas from said         container of oxidant gas to the second injection device of said         injection and cooling system;     -   a container of liquid solution S₃; and     -   third means devised to convey the liquid solution S₃ from said         container of liquid solution S₃ to the third injection device of         said injection and cooling system.

In the treatment installation according to the invention, the container of liquid solution S₁ may be of any shape and volume. It may be made of a material suitable for the nature of the liquid solution S₁. For example, such a material may be a metal, a ceramic or an alloy, particularly a non-oxidising alloy such as stainless steel.

The solution S₁ used within the scope of the present invention may be any liquid solution, advantageously organic, liable to contain at least one organic, toxic, harmful, corrosive and/or radioactive compound. The term “organic, toxic, harmful, corrosive and/or radioactive compound” denotes at least one element chosen from the heavy metals; radioactive elements and organic elements. By way of non-limiting examples, these compounds are chosen from the group consisting of chlorine, fluorine, sulphur, zinc, phosphorus, mercury, lead, cadmium, arsenic, phenol, cyanides, ferrocyanides, oxalates, humic acids, strontium, ruthenium, caesium, a emitters, such as americium, plutonium and uranium and mixtures thereof. The solution S₁ may be presented in the form of an organic liquid, pure or in a mixture, a radioactive liquid, an emulsion, a micro-emulsion, an aqueous solution, a suspension of particularly organic compounds in an aqueous solution, a liquid containing particles obtained from pulverising a solid or a hazardous liquid waste.

More particular, by the solution S₁ may be any type of solution containing organic matter optionally bound with minerals. Such a solution may be obtained from any civilian applications, nuclear or not, or any military applications, nuclear or not. By way of non-limiting examples, the solution S₁ may be chosen from the group consisting of a solution obtained from sewerage plants or sewerage plant sludge, wastewater, used oils, household liquid waste, medical or hospital liquid waste, industrial liquid waste and liquid waste from nuclear installations. In the present invention, the expressions “solution S₁”, “liquid solution S₁”, “liquid to be treated” or “solution to be treated” are equivalent and can be used interchangeably.

In the treatment installation according to the invention, the container of oxidant gas may be of any shape and volume. The oxidant gas may be chosen from the group consisting of oxygen, air, carbon dioxide and mixtures thereof. The oxidant gas is advantageously oxygen. The container of oxidant gas may be a cylinder of oxidant gas and particularly of pressurised oxygen.

In the treatment installation according to the invention, the container of liquid solution S₃ may be of any shape and volume. It may be made of a material suitable for the nature of the liquid solution S₃. For example, such a material may be a metal, a plastic, a ceramic or an alloy, particularly a non-oxidising alloy such as stainless steel.

In a first embodiment, the container of liquid solution S₃ is a reactor containing a solution S₂ different to the liquid solution S₁ to be treated. In the treatment method according to the present invention described hereinafter, the plasma is submerged in this reactor and thereof in this solution S₂. This embodiment enables a second passage in the plasma core of any organic compounds still present in the reactor solution and as such makes it possible to increase the organic compound destruction rate further.

As explained in the international application WO 2011/064361, the solution S₂ wherein the plasma is submerged carries out the cooling of the reactor without necessarily requiring additional elements for cooling the walls of the reactor. This solution S₂ also has a role in the treatment of gas emissions since it performs the quenching, dust extraction and neutralisation of the gases produced and the condensation of the volatile substances produced. The solution S₂ thus acts as a cooler, filter and scrubbing column.

The solution S₂ is an aqueous or saline solution and advantageously water. The solution S₂ may further contain at least one additive ensuring the destruction of residual organic matter. Such an additive is a catalyst ensuring advanced degradation of residual organic matter. These catalysts may, for example, activate Fenton reactions activated by the plasma radiation. They may consist of Fenton reagents ensuring radical production in plasma radiation. One particular example of such catalysts consists of metal ions and particularly ferrous ions enabling the production of extremely oxidant .OH radicals, the ferric ions produced being regenerated into ferrous ions by UV radiation. The use of a Fenton type reaction inside the reactor using UV radiation from the plasma torch or a further device offers the advantage of providing a means to destroy residual organic matter, this type of reaction being suitable for the treatment of organic substances in very small quantities typically of the order of one ppm.

Furthermore, the pH of the solution S₂ may be maintained at a value close to neutrality. In the present invention, the expressions “solution S₂”, “liquid solution S₂” and “reactor solution” are equivalent and can be used interchangeably.

The solution S₂ is not only different from solution S₁ but also does not correspond to a liquid solution from the treatment of particularly liquid waste such as a solution S₁ or resulting from such a treatment, such as, for example a solution containing partially treated waste liable to be obtained from a prior treatment of liquid waste, a molten bath obtained from the treatment of waste, a metal layer of such a molten bath or a layer of slag of such a molten bath. The definition of the solution S₂ above obviously includes when the latter is used i.e. when the plasma is submerged therein and prior to the injection of the solution S₁.

In a further embodiment, the container of liquid solution S₃ and the reactor containing a solution S₂ different to the liquid solution S₁ as defined above are two different elements. In other words, the treatment installation according to the present invention further has a reactor containing a solution S₂ different to the liquid solution S₁ and as defined above. In this embodiment, the liquid solution S₃ contained in the container of solution S₃ is typically an aqueous or saline solution and advantageously water.

Regardless of the embodiment, the reactor of the installation according to the invention may be of any shape and volume. As described in the international application WO 2011/064361, the solution S₂ carries out the cooling of the reactor, the latter thus does not necessarily need to be made of a material suitable for withstanding very high temperatures as it is cold. Advantageously, it is made of stainless steel.

The first means devised to convey the liquid solution S₁ from said container of liquid solution S₁ to the first injection device of said injection and cooling system may be any means suitable for conveying a liquid from one compartment to a different compartment. Of these means, mention may be made of liquid supply pumps and hydrostatic pressure liquid supply pumps. These means are fluidically connected to the container of liquid solution S₁ and/or to the first injection device of said injection and cooling device by piping made of flexible material or rigid material.

The second means devised to convey the oxidant gas from said container of oxidant gas to the second injection device of said injection and cooling system may be any means suitable for conveying a gaseous fluid from one compartment to a different compartment, such as, for example, gas supply pumps and relief valves. These means are fluidically connected to the container of oxidant gas and/or to the second injection device of said injection and cooling system by piping made of flexible material or rigid material.

The third means devised to convey the liquid solution S₃ from said container of liquid solution S₃ to the third injection device of said injection and cooling system may be any means suitable for conveying a liquid fluid from one compartment to a different compartment. Of these means, mention may be made of liquid supply pumps and hydrostatic pressure liquid supply pumps. These means are fluidically connected to the container of liquid solution S₃ and/or to the third injection device of said injection and cooling device by piping made of flexible material or rigid material.

The treatment installation according to the present invention may further comprise a device generating ultraviolet radiation. It is clear that this device is different from the plasma torch present in said installation. Any UV radiation system i.e. any system capable of emitting radiation wherein the wavelength range is in the near-ultraviolet range is suitable for use within the scope of the present invention. Mention may be made of a mercury vapour lamp in the form a “neon” type tube, a sodium vapour lamp, a luminescent semiconductor element, a light-emitting diode (LED). This device generating ultraviolet radiation makes it possible to regenerate the Fenton reaction catalysts, present in the solution S₂ of the reactor. When the treatment installation according to the invention does not comprise such a device generating ultraviolet radiation, it is the plasma that regenerates the Fenton reaction catalysts, present in the solution S₂ of the reactor.

The treatment installation according to the present invention may further comprise at least one or a plurality of additional elements such as those described for the installation according to the international application WO 2011/064361. Advantageously, this or these elements are chosen from the group consisting of (i′) means devised to apply an electrical current or a given potential to the plasma torch and more particularly to the electrodes forming this plasma torch, (ii′) means devised to supply the plasma torch with a plasma-forming gas and optionally a secondary gas, (iii′) a condenser, (iv′) an air filter, (v′) a device for cooling the solution S₂, (vi′) a device for filtering the solution S_(z), (vii′) means devised to control and adjust the pH of the solution S₂ and (viii′) means devised to add an acid or a base to the solution S₂.

The means devised to supply the plasma torch with a plasma-forming gas and optionally a secondary gas may be any means suitable for conveying a gaseous fluid into a compartment such as gas supply pumps. These means are connected to the plasma torch by piping made of flexible material or rigid material. Furthermore, the means suitable for supplying the plasma torch with at least one plasma-forming gas and optionally with at least one secondary gas may involve channels opening out between the anode and the cathode of the plasma torch and/or channels provided in the anode and/or the cathode.

When the treatment installation according to the present invention is operating, the gases generated following the gasification, combustion and/or oxidation bubble in the solution S₂ where they are quenched and purified of the dust thereof and neutralisable chemical species such as HCl, SO₂, SO₃, NO₂, NO₃ and P₂O₅. Before being discharged outside the device and particularly in the outside environment, they advantageously pass through a condenser and optionally through a filter. As such, the installation according to the present invention may comprise a condenser and optionally an air filter. Advantageously, the condenser and optionally the filter are mounted in the upper part of the reactor.

The condenser which also acts as a demister suitable for use within the scope of the present invention is advantageously a separated fluid condenser wherein a different fluid from the combustion gases and particularly a coolant fluid from a coolant device is kept at a temperature below that of the gas(es) entering the combustion chamber. The condenser suitable for use within the scope of the present invention may be a tubular heat exchanger or evaporator type condenser.

Any type of air filter is suitable for use at the outlet of the condenser within the scope of the present invention. However, in order to ensure high-efficiency filtration, an activated carbon type filter, glass microfibre filter or polytetrafluoroethylene filter can be used. By way of examples, mention may be made of a Megalam® panel filter or a Micretain® air filter.

The operation of the plasma torch and the gasification, combustion and/or oxidation of the components of the solution S₁ cause overheating of the solution S₂. Consequently, in order to reduce the saturating vapour pressure, the installation according to the present invention may comprise a device for cooling the solution S₂ i.e. system suitable for carrying out the cooling of the solution S₂. Furthermore, the installation according to the present invention may further comprise a device for filtering the solution S₂ i.e. a system suitable for carrying out the filtration of the solution S₂.

As such, the installation according to the present invention advantageously comprises an exchanger equipped upstream with a filter. The exchanger suitable for use within the scope of the present invention is a double-flow type heat exchanger wherein the solution S₂ exchanges heat with another liquid or gaseous flow so as to keep the temperature of the solution S₂ at a level limiting the vapour pressure at the surface of the reactor. This heat exchanger may be an exchanger in the form of a U-shaped tube, a horizontal or vertical tubular exchanger, a coil exchanger or a plate exchanger.

A filter is advantageously placed upstream from the exchanger to retrieve the dust from the combustion and any solid from the precipitation of the minerals present in the solution S₁. The filter used within the scope of the device according to the invention comprises at least one membrane advantageously of the nanofiltration, microfiltration or ultrafiltration type. These membranes are defined by pore sizes less than the average particle size of the dust and solids, conventionally from the order of one micrometre to some ten nanometres.

During the treatment, the solution S₂ may become acidic or basic according to the circumstances. Also, the device according to the present invention may further comprise means devised to control and adjust the pH of the solution S₂.

These means may comprise an electrode for measuring the pH placed in the reactor or in an external circuit to the reactor but connected thereto. The pH may be measured continuously or intermittently. The electrode for measuring the pH is connected, directly or indirectly, to means devised to add an acid or a base to the solution S₂.

The present invention further relates to a method for the treatment of a solution S₁ as defined above comprising a step consisting of injecting said solution S₁ into (i.e. in the core of) a plasma generated using a plasma torch as defined above and submerged in a second liquid solution hereinafter referred to as solution S₂ different from solution S₁ as defined above.

The term “treatment of a solution S₁” denotes within the scope of the present invention reducing the quantity of organic, toxic and/or harmful compounds as defined above and stabilising those which may be corrosive and/or radioactive, these compounds being present in the solution S₁ prior to the treatment according to the invention. This reduction may involve removing these compounds and/or converting same into less harmful compounds. Advantageously, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or even all of the chemical compounds initially contained in the solution S₁ are removed and/or converted into less harmful compounds following the treatment according to the invention.

The method according to the present invention advantageously comprises steps consisting of:

a) generating a plasma from a plasma torch equipped with an injection and cooling system as defined above;

b) submerging the plasma generated in step (a) in a solution S₂ as defined above;

c) introducing an oxidant gas in the vicinity of the plasma via the second injection device of said injection and cooling system;

d) introducing the solution S₃ as defined above in the vicinity of the plasma via the third injection device of said injection and cooling system; and

e) introducing the solution S₁ as defined above into the plasma submerged in this way via the first injection device of said injection and cooling system.

Typically, steps (a), (b) and (c) are carried out in succession. Steps (c), (d) and (e) may be carried out in succession or simultaneously.

Step (a) of the method according to the invention consists of generating a plasma and particularly a blown arc plasma from a plasma torch as defined above. Advantageously, an electric discharge is produced at the plasma torch consisting of electrodes while a plasma-forming gas passes between these electrodes which generates the plasma.

The plasma-forming gas suitable for use may be any gas known to those skilled in the art. It may vary according to the plasma torch technology used. Within the scope of the present invention, the plasma-forming gas comprises an oxidant gas required for plasma reactivity and/or a neutral gas required for the protection of the cathode of the torch.

In a first alternative embodiment, the plasma-forming gas only comprises one oxidant gas. This alternative embodiment uses a torch not requiring a neutral gas for protection. The oxidant gas may thus be chosen in the group consisting of oxygen, air, carbon dioxide and mixtures thereof. The oxidant gas is advantageously oxygen.

In a second alternative embodiment, the plasma-forming gas comprises an oxidant gas as defined above and a neutral gas. The neutral gas is particularly chosen in the group consisting of argon, helium, nitrogen and mixtures thereof. Advantageously, the plasma obtained in chosen in the group consisting of an argon/oxygen plasma, a helium/oxygen plasma, and a nitrogen/oxygen plasma.

In a third alternative embodiment corresponding particularly to the case where a non-oxidising gasification is sought during step (c) of the method, the plasma functions merely with the neutral gas as defined above and particularly with argon and does not require the addition of oxygen. If oxidation is required to destroy the organic compounds contained in the solution S₁, then an oxygen stream may be added in order to produce a neutral gas/oxygen plasma, this oxygen stream being supplied via the second injection device of said injection and cooling system as defined above.

In a fourth alternative embodiment, the plasma-forming gas is an exhaust gas recycled to the plasma torch. Such a gas advantageously comprises the compounds CO₂/O₂/Argon. In this alternative embodiment, torch technologies routinely using cooled copper anodes and cathodes may be envisaged. Further metals such as tungsten may be envisaged according to the operating modes chosen. As such, in this fourth embodiment, the plasma used recycles all or part of the gases emitted by the method as plasma-forming gases.

Step (b) of the method according to the present invention consists of filling the reactor wherein the plasma was generated during step (a) with the solution S₂. During the filling of the reactor, the latter is not completely filled with the solution S₂.

The solution S₂, during step (b), has a temperature between 20 and 60° C. and, particularly has a temperature regulated around 30° C.±5° C. Consequently, the relatively high temperature of the reactor following step (a) is lowered, advantageously to the temperature of the solution (S₂). Therefore, the term “cold reactor” may be used in the present invention.

Once the plasma has been initiated, the reactor should be filled rapidly to prevent overheating of the system.

Step (c) of the method according to the present invention consists of re-enriching the plasma with oxidant gas. Within the scope of the present invention, this re-enrichment is performed via the second injection device of said injection and cooling system.

The rate of introduction of the oxidant gas will be dependent on the power of the plasma used and the nature of the solution S₁. According to the circumstances, it may attain several tens of litres per hour. The introduction of oxidant gas during step (c) may be performed continuously or sequentially by alternating phases with or without the introduction of oxidant gas.

Step (c) of the method according to the present invention may last from a few minutes to several hours or even several days. As such, step (c) of the method according to the present invention may be carried out 24 hours a day for times consistent with the lifetime of the plasma torch.

Step (d) of the method according to the present invention consists of contacting the solution S₃ as defined above with the plasma and optionally the combustion gases. Within the scope of the present invention, this contacting is performed via the third injection device of said injection and cooling system.

The rate of introduction of the solution S₃ will be dependent on the power of the plasma used and the nature of the solution S₃. According to the circumstances, it may attain several tens of litres per hour. The introduction of the solution S₃ during step (d) may be performed continuously or sequentially by alternating phases with or without the introduction of solution.

Step (d) of the method according to the present invention may last from a few minutes to several hours or even several days. As such, step (e) of the method according to the present invention may be carried out 24 hours a day for times consistent with the lifetime of the plasma torch.

Step (e) of the method according to the present invention consists of contacting the solution S₁ with the plasma core so that the treatment as defined above takes place instantaneously. Within the scope of the present invention, this introduction is performed via the first injection device of said injection and cooling system.

The rate of introduction of the solution S₁ will be dependent on the power of the plasma used and the nature of the solution S₁. According to the circumstances, it may attain several tens of litres per hour. The introduction of solution S₁ during step (e) may be performed continuously or sequentially by alternating phases with or without the introduction of solution.

Step (e) of the method according to the present invention may last from a few minutes to several hours or even several days. As such, step (e) of the method according to the present invention may be carried out 24 hours a day for times consistent with the lifetime of the plasma torch.

As explained above, the gasification, combustion and/or oxidation reaction of the compounds of solution S₁ takes place instantaneously in the plasma from the contacting of the solution S₁ therewith.

After steps (c), (d) and (e) of the method according to the present invention, the dissociated gases once released from the plasma must be rapidly neutralised and quenched particularly to prevent the formation of toxic complex molecules such as furans or dioxins. The solution S₂ carries out these functions. Similarly, the dust and volatile compounds from the gasification, combustion and/or oxidation reaction are respectively removed and condensed by means of the solution S₂.

The method according to the present invention comprises an additional step consisting of filtering, cooling and/or neutralising said solution S₂. It should be pointed out that the operation of the plasma torch and the reactions occurring during steps (c), (d) and (e) and particularly during step (e) of the method according to the present invention may cause overheating of the solution S₂ situated in the reactor.

Also, in order to reduce the saturating vapour pressure, the method according to the present invention may comprise an additional step consisting of cooling the solution S₂. This additional step may take place during or after any one of steps (c), (d) and (e) of the method. Advantageously, the cooling of the solution S₂ is implemented simultaneously with step (c) of the method. Alternatively, the cooling of the solution S₂ is implemented simultaneously with step (e) of the method.

Any system suitable for lowering the temperature of a liquid is suitable for use for this cooling step. Advantageously, this step uses a parallel treatment loop involving an exchanger or a cooling tower.

A filter blocking the mineral particles from the treatment and destruction of the solution S₁ is advantageously fitted on the loop, upstream from the exchanger used to cool the solution S₂.

Finally, when the treatment method according to the present invention is completed, the reactor is drained of the solution S₂ thus allowing the plasma to emerge for a brief time, the time required to dry the parts topping the torch in order to prevent the solution S₂ from entering the nozzle thereof. This emergence time produces normal overheating of the reactor. The time during which the plasma is emerged should be quick but sufficient to dry the parts topping the torch. It may be between 10 sec and 5 min.

Once the torch has been switched off, the plasma-forming gas supply should be maintained in order to dry the torch completely. This supply may be maintained for a time greater than 10 min.

Further features and advantages of the present invention will emerge for those skilled in the art on reading the examples hereinafter given by way of illustration and not restriction, with reference to the appended figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a general and schematic view of a waste treatment device according to the international application WO 2011/064361 and according to the present invention with, as an insert, the schematic representation of the injection and cooling system according to the present invention.

FIG. 2 is a more detailed view of a blown arc plasma torch suitable for being used in a device for the treatment of liquid waste according to the present invention.

FIG. 3 relates to the first injection device of the injection and cooling system according to the present invention. FIG. 3A is a longitudinal sectional partial schematic view of the first injection device of the injection and cooling system arranged on the plasma torch. FIG. 3B is a perspective partial schematic view of the first injection device of the injection and cooling system.

FIG. 4 relates to the second injection device of the injection and cooling system according to the present invention. FIG. 4A is a longitudinal sectional partial schematic view of the first and second injection devices of the injection and cooling system arranged on the plasma torch. FIG. 4B is a perspective partial schematic view of the second injection device of the injection and cooling system.

FIG. 5 relates to the third injection device of the injection and cooling system according to the present invention. FIG. 5A is a longitudinal sectional partial schematic view of the first, second and third injection devices of the injection and cooling system arranged on the plasma torch. FIG. 5B is a perspective partial schematic view of the third injection device of the injection and cooling system.

FIG. 6 relates to the cooling device of the injection and cooling system according to the present invention. FIG. 6A is a longitudinal sectional partial schematic view of the first, second and third injection devices and the cooling device of the injection and cooling system arranged on the plasma torch. FIG. 6B is a perspective partial schematic view of the cooling device of the injection and cooling system.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS I. Device

Hereinafter, the terms “axial” and “radial” are defined with respect to the axis of the plasma torch AA′.

FIG. 1 illustrates in the right-hand section thereof the operating principle of the method as described in the international application WO 2011/064361 [5] and as implemented in the present invention.

FIG. 1 illustrates the description provided hereinafter. The present invention is based on the use of a blown arc plasma 1 submerged in a reactor of cylindrical shape and having a volume of 50 L, filled with water 2. The liquid product to be treated 3 such as a mixture of tributyl phosphate (TBP) and dodecane is introduced into the plasma via the first injection device of the injection and cooling system according to the invention. Once in the plasma, the liquid is instantaneously brought to a very high temperature of the order of 2000° C. in the presence of oxygen, resulting in the total destruction of the organic matter.

FIG. 2 represents the plasma torch used. It consists of a conventional plasma torch wherein a refractory metal cathode 10 particularly made of tungsten, of conical shape, protected by an argon stream generates an electric arc to an anode 11. The anode 11 is presented in the form of a copper sheath 10 cm in length and 10 mm in diameter. This arc is blown by an argon and oxygen stream. The plasma torch used has a device 12 for cooling by internal water circulation the diaphragm and the anode.

FIGS. 3A and 3B represent the first injection device 13 of the injection and cooling system according to the invention. This first device is placed at the outlet of the plasma torch and particularly in the vicinity of the anode 11. More particularly, this first device is presented in the form of a cooled metal part made of Inconel® measuring 26 mm in height, cylindrical with a circular cross-section and having a central recess 14 of cylindrical shape with a circular cross-section. This central recess 14 forms part of the cavity of the injection and cooling system. This first device has an attachment flange 15 projecting radially outwards having at least one orifice 16 for the passage of a tie rod. Advantageously, the attachment flange has four orifices 16 for the passage of tie rods. This first device 13 has a circulation chamber 17 of the liquid to be treated, at least one intake channel 18 of the liquid to be treated leading to said circulation chamber 17 and at least one injection channel 19 of the liquid to be treated connected to said circulation chamber 17 and leading to the central recess 14 i.e. in the cavity of the injection and cooling system. The intake channel 18 of the liquid to be treated leads via at least one orifice 20 to the side wall of the first injection device 13. The injection channel 19 is oriented towards to the outlet orifice of the plasma 21. The liquid to be treated is injected at a rate of a few centimetres per second, this rate varying according to an adjustable flow rate between 0 and 4 litres per hour.

FIGS. 4A and 4B represent the second injection device 22 of the injection and cooling system according to the invention. This second device 22 is placed on and in contact with the first injection device 13. More particularly, this second device 22 is presented in the form of a metal part made of Inconel®, measuring 22 mm in height, cylindrical with a circular cross-section and having a central recess 23. The walls defining the central recess 23 have an internal radial surface of tapered shape. In fact, this second device 22 acts as a divergent at the nozzle outlet. This second device 22 has an oxidant gas circulation chamber 24, at least one oxidant gas intake channel 25 leading to said circulation chamber 24 and at least one oxidant gas injection channel 26 connected to said circulation chamber 24 and leading to the central recess 23 i.e. in the cavity of the injection and cooling system. The oxidant gas intake channel 25 leads via at least one orifice 27 to the side wall of the second injection device 22. The injection channel 26 of a few mm in diameter is oriented towards the third injection device 28. The second injection device has at least one orifice 29 for the passage of a tie rod. Advantageously, it has four orifices 29 for the passage of tie rods.

FIGS. 5A and 5B represent the third injection device 28 of the injection and cooling system according to the invention. This third device 28 is placed on and in contact with the second injection device 22. More particularly, this third device 28 is presented in the form of a metal part made of stainless steel, measuring 22 mm in height, cylindrical with a circular cross-section and having a central recess 30 of cylindrical shape with a circular cross-section and having a central recess 30. The walls defining the central recess 30 have an internal radial surface of tapered shape. This third device 28 has a circulation chamber 31 of the solution S₃ as defined above and particularly water, at least one intake channel 32 of the solution S₃ and particularly water leading to said circulation chamber 31 and at least one injection channel 33 of the solution S₃ and particularly water connected to said circulation chamber 31 and leading to the central recess 30 i.e. in the cavity of the injection and cooling system. The intake channel 32 of the solution S₃ and particularly water leads via at least one orifice 34 to the side wall of the third injection device 28. The injection channel 33 is oriented towards the cooling device 35. The third injection device has at least one orifice 36 for the passage of a tie rod. Advantageously, it has four orifices 36 for the passage of tie rods.

FIGS. 6A and 6B represent the cooling device 35 of the injection and cooling system according to the invention. This cooling device 35 is presented in the form of a metal part made of stainless steel, measuring 107 mm in height, having the shape of a shaft (or sheath or nozzle) and having a central recess in the form of a shaft (or sheath or nozzle) wherein the internal walls define a cylindrical central recess 37 having a circular cross-section. In the wall thereof, the cooling device 35 has a channel 38 or a plurality of channels for circulating a coolant such as water. This cooling device 35 has an attachment flange 39 projecting radially outwards having at least one orifice 40 for the passage of a tie rod. Advantageously, the attachment flange has four orifices 40 for the passage of tie rods.

The injection and cooling system according to the invention has at least one tie rod or bolt which jointly provides the attachment and fastening of the devices 13, 22, 28 and 35 to one another and with the plasma torch. These tie rods pass through the orifices 16, 27, 34 and 40.

The treatment method using a blown arc plasma 1 obtained from a plasma torch equipped with an injection and cooling system submerged in a reactor filled with an aqueous solution 2. This aqueous solution may further contain in solubilised form metal ions and hydrogen peroxide in order to carry out a Fenton reaction maintained by the UV radiation from the plasma torch.

After instantaneous gasification and decomposition in the argon-oxygen plasma plume, the residual or partially oxidised organic compounds are subjected to a second oxygen stream introduced via the second injection device 22 of the injection and cooling system according to the invention.

The combustion gases are then quenched with water so that they reach a temperature level suitable for establishing the chemical equilibriums compatible with emission requirements. The addition of water which may also be the aqueous solution of the reactor is carried out by means of the third injection device 28 of the injection and cooling system according to the invention.

The gases then pass though the cooling device 35 of the injection and cooling system according to the invention wherein they finish cooling and adopt the final composition thereof before entering the core of the aqueous solution wherein they are instantaneously quenched.

During bubbling, the gases are purified of the dust thereof and neutralisable chemical species such as HCl, HF, SOx, NOx, P₂O₅, etc. They then pass through a condenser 4 which also acts as a demister and are discharged outside. According to purification level sought, the gases may be subjected to ultra-high-efficiency filtration 7 to prevent any particle emissions.

The aqueous solution of the reactor may contain ions suitable for catalysing the optimisation of the degradation of residual compounds at very low levels. For example, ferrous ions Fe²⁺ associated with the presence of hydrogen peroxide may be added so as to catalyse the formation of OH radicals ensuring the destruction of residual organic matter. The Fe³⁺/Fe²⁺ transition may then be performed by the UV radiation from the arc plasma.

The operation of the plasma torch and the combustion of the organic matter cause overheating of the aqueous solution situated in the reactor. In order to reduce the saturating vapour pressure, the water is cooled in a loop via an exchanger 6. The temperature thereof is maintained at a level limiting the vapour pressure at the reactor surface. The cooling circuit is equipped upstream from the exchanger 6 with a filter 5 retrieving the solids from the precipitation of the minerals present in the effluents to be treated. This filtration-cooling loop extracts the solution into the lower part of the reactor and reintroduces same into the upper part thereof.

During the treatment, the reactor solution may become acidic or basic according to the circumstances. Online monitoring of the pH 8 enables continuous adjustment of the value thereof by adding an acid of a based according to the circumstances 9. This adjustment should, if applicable, account for the chemical requirements imposed by the use of the Fenton reaction.

II. Operation and Performances

The experimental development phases used to design the enhancements described in the present invention clearly illustrate the various enhancement steps.

The tests were conducted on a solution to be treated comprising a mixture of tributyl phosphate (TBP) and dodecane, this mixture having the dual specificity of having a high NCV (≈10 kW·h·L⁻¹). This solution was injected into the plasma at a feed rate of 3 L·h⁻¹.

The plasma torch operates at a flow rate of 30 NL·min⁻¹ of argon and 180 NL·min⁻¹ of oxygen in the arrangement represented in FIG. 1.

The measurements made on the composition of the solution show destruction rates greater than 99.5%. The positioning of the various stages at the plasma torch outlet modifies the gas emission composition substantially. The CO and CO₂ contents, representative of the level of oxidation of the gas mixture, were monitored in the following four scenarios:

Untreated Injection into Plasma Flame:

CO composition at outlet: 12%

CO₂ composition at outlet: 4%

Injection into Plasma Flame Followed by Re-Enrichment with O₂ (40 NL·Min⁻¹):

CO composition at outlet: 9%

CO₂ composition at outlet: 6%

Note herein that adding oxygen provides superior oxidation but also partial cooling of the gas enabling a thermal shift of the CO/CO₂ equilibrium.

Injection into Plasma Flame Followed by Re-Enrichment with O₂ (40 NL·Min⁻¹) and Cooling in Nozzle:

CO composition at outlet: 8%

CO₂ composition at outlet: 9%

The cooling provided by the outlet nozzle is not sufficient as the CO level is still well above emission standards.

Injection into Plasma Flame Followed by Re-Enrichment with O₂ (40 NL·Min⁻¹), Addition of Cooling Water (0.3 L·Min⁻¹) and Cooling in Nozzle:

CO composition at outlet: 0.2%

CO₂ composition at outlet: 8%

This last test demonstrates the effectiveness of the technological enhancements applied.

REFERENCES

-   [1] Patent application EP 0,469,737 (Tioxide Group Services Limited)     “Destruction process” published on 5 Feb. 1992. -   [2] Alekseev N. V., Samokhin A. V., Belivtsev A. N. and     Zhavoronkova V. I., (2000) “Thermal-Plasma Jet Oxidation of Phenol     in Aqueous Solutions”, High Energy Chemistry, Vol. 34, No 6, pp.     389-393. -   [3] Fortin L., Soucy G., Kasireddy V., Bernier J.-L., Boulos M.     I (1999) “The Use of Thermal Plasma for Wastewater Treatment”, 14th     International Symposium on Plasma Chemistry—ISPC'14, Prague (Czech     Republic), pp. 2387-2392. -   [4] International application WO 97/22556 (Alcan International     Limited) “Thermal Plasma Reactor and Wastewater Treatment Method”     published on 26 Jun. 1997. -   [5] International application WO 2011/064361 (CEA) “Method and     device for the treatment of waste through injection into an immersed     plasma” published on 3 Jun. 2011. 

1. Injection and cooling system, intended to equip a plasma torch, having a cavity intended to contain plasma and combustion gas and comprising: a first injection device devised to inject, into said cavity, a liquid solution to be treated hereinafter referred to as solution S₁, a second injection device arranged against said first injection device and devised to inject, into said cavity, an oxidant gas, a cooling device devised to cool the gas(es) contained in said cavity, said system comprising a third injection device inserted between said second injection device and said cooling device and devised to inject, into said cavity, a liquid solution different to the liquid solution to be treated hereinafter referred to as solution S₃ and said four devices being hollow, coaxially aligned and defining said cavity, said system successively comprising said first injection device, said second injection device, said third injection device and said cooling device, said devices being placed on top of one another.
 2. Injection and cooling system according to claim 1, characterised in that said first injection device comprises at least one first channel leading to said cavity and devised to convey said solution S₁ therein.
 3. Injection and cooling system according to claim 1 or 2, characterised in that said second injection device comprises at least one second channel leading to said cavity and devised to convey said oxidant gas therein.
 4. Injection and cooling system according to any one of claims 1 to 3, characterised in that said third injection device comprises at least one third channel leading to said cavity and devised to convey said solution S₃ therein.
 5. Injection and cooling system according to any one of claims 1 to 4, characterised in that said cooling device comprises at least one sheath cooled by internal water circulation.
 6. Plasma torch equipped with an injection and cooling system according to any one of claims 1 to
 5. 7. Installation for the treatment of a liquid solution S₁ comprising: a plasma torch equipped with an injection and cooling system according to any one of claims 1 to 5; a container of liquid solution S₁; first means devised to convey the liquid solution S₁ from said container of liquid solution S₁ to the first injection device of said injection and cooling system; a container of oxidant gas; second means devised to convey the oxidant gas from said container of oxidant gas to the second injection device of said injection and cooling system; a container of liquid solution S₃; and third means devised to convey the liquid solution S₃ from said container of liquid solution S₃ to the third injection device of said injection and cooling system.
 8. Treatment installation according to claim 7, characterised in that said container of liquid solution S₃ is a reactor containing a solution S₂ different to the liquid solution S₁ to be treated.
 9. Treatment installation according to claim 7, characterised in that said installation further has a reactor containing a solution S₂ different to the liquid solution S₁.
 10. Treatment installation according to any one of claims 7 to 9, characterised in that said installation further comprises a device generating ultraviolet radiation.
 11. Treatment installation according to any one of claims 7 to 10, characterised in that said installation further comprises at least one or a plurality of additional elements chosen from the group consisting of (i′) means devised to apply an electrical current or a given potential to the plasma torch and more particularly to the electrodes forming this plasma torch, (ii′) means devised to supply the plasma torch with a plasma-forming gas and optionally a secondary gas, (iii′) a condenser, (iv′) an air filter, (v′) a device for cooling the solution S₂, (vi′) a device for filtering the solution S₂, (vii′) means devised to control and adjust the pH of the solution S₂ and (viii′) means devised to add an acid or a base to the solution S₂.
 12. Method for the treatment of a solution S₁ comprising a step consisting of injecting said solution S₁ into a plasma generated using a plasma torch as defined in claim 6 and submerged in a solution S₂ different from said solution S₁.
 13. Method according to claim 12, characterised in that it comprises steps consisting of: a) generating a plasma from a plasma torch equipped with an injection and cooling system according to any one of claims 1 to 5; c) introducing an oxidant gas in the vicinity of the plasma via the second injection device of said injection and cooling system; d) introducing the solution S₃ in the vicinity of the plasma via the third injection device of said injection and cooling system; and e) introducing the solution S₁ into the plasma submerged in this way via the first injection device of said injection and cooling system. 